1. Technical Field
This invention relates to the identification of sulfonation by-products in polymeric sulfonate, and more particularly, to the identification of and quantification of such sulfonation by-products by ion chromatography.
2. Description of Related Art
Polymeric sulfonates, such as polyvinyl sulfonates, are effectively utilized to inhibit the formation of scale, particularly inorganic sulfate such as barium sulfate, in subterranean formations. Polymeric sulfonates are conventionally polymerized from commercially available solutions containing a monomer in the presence of a suitable catalyst. For example, polyvinyl sulfonate can be polymerized from a commercially available, dilute, e.g., 25-50 weight percent, aqueous solution of vinylsulfonic acid, sodium salt, in the presence of a suitable catalyst, such as ammonium persulfate or sodium bisulfite. The resultant aqueous polymerization solution contains undesirable by-products of sulfonation, such as sulfate and/or chloride ions and hydroxyethyl sulfonate, and unreacted vinylsulfonic acid sodium salt monomer, in addition to polyvinyl sulfonate. The presence of such undersirable by-products can be extremely deleterious when a polymeric sulfonate is used as a scale inhibitor. Thus, solvents, such as methanol, ethanol and acetone, have been employed to remove undesirable by-products of sulfonation from aqueous polymerization solutions containing polymeric sulfonates. Typical solvent removals are found in German Patent No. 1 495 761 to Hoechst and U.S. Pat. No. 4,995,982 to Barthorpe.
Typical deleterious polymeric sulfonate contaminants are sulfate, chloride, hydroxyethylsulfonate (HES), and sodium vinylsulfonate (SVS). Sulfate ions cannot be identified or quantified by any of the conventional methods, such as size exclusion chromatography, gravimetric turbidimetric precipitation techniques, since compounds, such as ethionic acids, act as sulfate does in such techniques. However, ion chromatography can be used to identify sulfate ion. Ion chromatography is a separation technique which employs a mobile phase, i.e., an eluant, to transport a liquid sample to be analyzed through a stationary phase, i.e., an analytical column. The column has ion exchange groups bound thereto to ionically attract those components in a given liquid sample which have an affinity for the ion exchange groups. However, analysis of polymeric sulfonate samples for contaminants such as sulfate ion by ion chromatography has proved troublesome since the polymeric sulfonate tends to plug the column thereby restricting flow of the sample. Thus, a need exists for a method of analyzing a sample of a polymeric sulfonate by ion chromatography to determine the amount of certain deleterious by-products of sulfonation contained therein.
It is an object of the present invention to provide a method of quantifying the deleterious by-products of sulfonation in a polymeric sulfonate sample by ion chromatography.
It is a further object of the present invention to provide a method of determining the degree by which such deleterious by-products of sulfonation are removed by a given washing process.
It is another object of the present invention to provide a process for simultaneously identifying and quantifying several deleterious by-products of sulfonation present in a partly aqueous solution.